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GCSE: Electricity and Magnetism
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- Marked by Teachers essays 19
- Peer Reviewed essays 18
Draw stress and strain graphs for the metal copper and the alloy constantan. Calculate the figures of young's modulus for copper and constantan. Discuss the physics involved.4 star(s)
I have included a diagram of the set-up (Figure 1) below which was used to obtain the results I was given. Figure 1 (SOURCE: AS PHYSICS CDROM) The experiment works by a G-Clamp holding the wooden block steady, this will place pressure on the wire to keep it steady at the clamped end. The cardboard bridges keep the wire straight and in place throughout its length. The pulley allows the wire to move freely along it to keep friction minimum. As load is increased this puts pressure on wire and it may extend in length, which is the variable I will be measuring.
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The time left for the alcohol to burn will also affect the results, as the longer it is left to burn, the more energy will be released. Finally, the height of the water above the flame will affect the results. As the energy is released, some of it will be dispersed into the air before reaching the water. With a larger distance between the water and the spirit burner, there would be more time for the energy to disperse, and the amount of energy in the water would be lower than if the water was closer to the spirit burner.
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By using this program, I will be able to achieve very precise results. Method: I will firstly collect the various equipment I will need which includes: A G clamp, wooden blocks, pulley, mass hangers with slotted weights, copper and constantan wire samples and a ruler. I will measure using a micrometer, the diameter of the wires and the length with a meter ruler. I will measure the length of the wires in metres and measure off very accurately to one decimal place.
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V I V = IR R= V/ I V= Potential difference in volts (V) I = Current in amps (A) R= Resistance in a unit is called an ohm () The graph below shows the relation between the current and the voltage of a conductor, showing that as the current increases the voltage increases. This is what is termed as Ohm's Law. In order to find the resistance of a conductor, the gradient of the graph is found out using the formula: Gradient of the graph = I/V Whereby R = 1/gradient FACTORS AFFECTING THE RESISTANCE OF A WIRE: There are four external factors that influence the resistance in a conductor.
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To investigate how the resistance, R, of a length of wire, l, changes with diameter, D and determine the resistivity of the material the wire used.4 star(s)
The length is also an issue as the longer the wire the higher the resistance because the electrons have to travel past more atoms and collisions between the electrons and the atoms are more likely then in shorter wires. Resistance should also be proportional to the length of the wires. So, I have decided on using a length of 1m. In a metal, conduction electrons are free to move the fixed positive ions, when a voltage is applied i.e. a battery source; the free electrons are repelled by the negative terminal and attracted to the positive one.
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Because the wire is longer, the chances of the electrons colliding with each other also increases, so this causes obstruction and resistance will increase. In this case, there will be different lengths of the wire measured, and the longest wire will have the highest resistance. (With the width kept the same). With more atoms, the more likely the moving electrons will collide with them, and so the flow would be less meaning a higher resistance. With more length, the chances of the neighbouring electrons colliding with each other should also increase.
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Resistance Aim: my main aim is to investigate the factors that affect the resistance in a conductor, in which here I am using a nichrome wire.3 star(s)
What we know about current already is that it is nothing but the rate of flow; however when the temperature rises the atoms also vibrate in their own balance more forcefully impending the flow of electric charges due to more frequent collisions. More electrons are available to conduct the current in the wire. Collision with lattice ions is less frequent. The current increases and the resistance decreases. However, the cross-section area will also have an effect, as the larger this is, the more charge can pass through it at the same time as it passes through a given length.
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This will give me a larger group of data than if I just increased one of them. I will need to use the preliminary tests to work out the gaps I will be increasing them by. Hypothesis I predict that, the length of the wire will be proportional to the resistance; therefore if the length of wire gets longer the resistance will get greater. My prediction is that the shorter the wire the higher current will be and the longer the wire the lower the current will be at each voltage section.
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This is because; the air trapped between two turns forms an insulating barrier that doesn't allow the passage of current, if the distance was more. > Strength of the electric current: To make an electromagnet function correctly electricity has to be passed through it. Therefore if the current is increase the strength of the magnet will increase and vice versa. > Number of turns of the coil: If the number of turns on the solenoid is increased then the strength of the magnet is increased and vice versa.
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Resistance Investigation. My aim in this investigation is to measure the amount of resistance in the different lengths of the wire.
However if the cross-sectional area of the wire causes the flow of the current of the electrons to retard then the resistance of the flow of electrons would increase as the electrons have less space to travel through. Another variable that could affect the resistance is the material that the wire consists of. If the wire is made of a single element then the electrons moving through the atoms will only be able to collide with the atoms of that element which would increase the flow of the current and decrease the resistance of the electrons.
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The smaller the cross-sectional area of the nichrome wire is e.g. 20swg, the fewer channels of electrons in the wire for current to flow and as a result of this the resistance will be high but having a lower area of wire leaves it more susceptible to a heating effect. However, when the cross -sectional area increases to a value of 36swg for example the resistance will decrease as there are more channels of electrons in the wire (This can be seen in the following diagrams; figure 1 and figure 2).
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Length- Length is the variable that I will be changing and will be basing my whole investigation around. As the length of the wire increases the resistance through the wire will also increase. This is because in a longer wire there is more electrons colliding with the metal ions as they travel along the wire than there would be in a shorter wire. This means that there are more collisions between the electrons and the metal ions which make the atoms vibrate more which makes the metal hotter.
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This is ohm's law, meaning that changing the voltage would also change the current by the same amount the voltage was changed by, therefore keeping resistance the same. This is shown by the formula I= V/R, where (I) is the current, (V) is the voltage and (R) is the resistance. Another factor that we can test is changing the diameter of the wire. A thinner wire would provide more resistance because there is less space for the electrons to pass, which would then cause the battery to work harder to push the wire around the circuit as there is more resistance.
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I had set up this investigation to see whether the voltage flowing through a light bulb affected the resistance. I conducted the investigation by setting up a simple circuit, which is illustrated by the circuit diagram below. Equipment - * Filament Light Bulb - To test the resistance of a filament light bulb * Connectors - To connect the circuit together * Power Supply - To power the circuit so the resistance can be calculated * Rheostat - A variable resistor so the voltage can be altered accurately (I had chose to use this because I could alter the voltage flowing through the current accurately)
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The in 1918 a polish scientist developed a method to produce single-crystal silicon. This is a semi-conductor which can be adapted to free electrons when it is exposed to a light source. Today PV cells are being used all over the world in everyday situations. There are villages in the US which get all their electricity from solar cells alone. There are both advantages and disadvantages to Photovoltaic cells; an advantage of PV cells is that they require daylight not direct sunlight.
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Variables Input: * Length of wire. * * Material of wire. * Width of wire. * Starting temperature of wire. Output: * Voltage across wire. � * Current in circuit. � * Temperature of wire. * Resistance of wire� The variable marked with a * will be varied, the other input variables will be kept constant. The output variable marked with a � will be measured. Predictions * The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free electrons, the particles making up the metal, and any impurities in the metal.
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Resistance of a wire - a number of experiments were carried out to determine different variables affected resistance.
Single length of constantan wire 5. Double length of constantan wire 6. Triple length of constantan wire 7. Single length of constantan wire (10cm, 20cm, 30cm) The conclusion drawn * Types of wire - Comparing wires made from different materials. It was found that each different type of wire had a different resistance. Therefore, it is fair to conclude that the resistance of a wire depends upon the resistivity of the wire, i.e. its ability to resist the flow of charge. * Thickness of wire - Comparing wires which had different thicknesses. It was found out that as the thickness of the wire increased the resistance decreased.
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Strategy The factor I have chosen to investigate the effect on resistance after changing the length of nichrome wire, whilst the current is consistently 0.2 amps. I have chosen this factor because if I would have chosen rho (material) I would be limited as to the things I could investigate: the highest or lowest resistance out of all materials tested. This would mean that I could only put my results in a bar chart as it is not continuous data and would mean I would be limited as to the conclusions I could extract from my findings.
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This will be kept constant because current will be kept constant. iii) Cross sectional area (thickness) - This will affect the resistance because as the area of the wire increases, the resistance will decrease because the electrons now have more space to travel and have better chances of avoiding collisions with the ions in the lattice and so the current can flow more efficiently. iv) Length of wire - Similarly if the wires length increases, then the electrons have a larger distance to travel.
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to the ratio of potential difference (voltage) across it (providing the temperature remains constant)", or... the current passing through a wire, at constant temperature, is proportional to the potential difference between its ends. This is the solution to working out the resistance of a wire, and is called Ohm's Law. He also put this discovery into a memorable formula: ... (V= P.D (volts), I=current (amps) & R=resistance (Ohms)). Using this formula, we can effortlessly work out the resistance by only working out the p.d and current (using a voltmeter and an ammeter), and then calculating the resistance.
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Thickness of the wire, 2. Length of the wire, 3. Material the wire is made out of and 4. Temperature of the wire. I have decided to investigated how length affects the resistance of a wire. So, to make this experiment fair I will keep thickness, material and temperature the same at all times in the experiment. The only variable that will change is going to be length of the wire. Also to make this test fair I will keep the supply at the same voltage and will make sure that this voltage is not to high so the wire could not overheat.
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A description of comparisons between the trends in the results of each experiment will be made and the ways in which the resistance of nickel-chrome wire changes as its length and diameter are adjusted, will also be evaluated. Before the experiment had begun, I predicted that concerning the first experiment, the longer wire the more the resistance and in the second experiment the thinner the wire the higher the resistance. This is because the electrons of a current flowing through short wire have less distance to travel and therefore have fewer collisions causing less resistance than they would get traveling further.
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An electromagnet can also be called a solenoid. The strength of an electromagnet is affected by number of factors. The main factors are: - Number of turns on the coil of wire around the core - Strength of the current applied - The material of the coil How does varying the number of turns on the coil affect the strength of an electromagnet? When electrons flow thought a wire, a magnetic field is created around the wire. Looping the wire increases the magnetic field and strengthens the magnet. When DC electricity is passed through a wire, a magnetic field rotates around the wire in a specific direction.
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Resistance is usually measured in ohms Ohms Law Ohms Law states that the current through a metallic conductor (e.g. wire) at a constant temperature is proportional to the potential difference (voltage). Therefore V I. This means that the resistance of a metallic conductor is constant providing that the temperature also remains constant. Furthermore, the resistance of a metal increases as its temperature increases. This is because at higher temperatures, the particles of the conductor are vibrating more quickly, therefore increasing the likelihood of collisions with the free electrons.
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Resistance slows down the electrical current flow therefore as the resistance increases the current decreases. All substances are made up of atoms, which have a nucleus that is made up of protons and neutrons which are surrounded by electrons. Protons are positively charged particles positioned in the nucleus of an atom. The nucleus is the central part of an atom that contains both positively charged protons and uncharged neutrons. Neutrons are a particle with no electrical charge found in the nucleus of most atoms. Its mass is similar to that of a proton. Electrons are a negatively charged particle orbiting in shells around the atomic nucleus.
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